The invention generally relates to a motion control system for driving a motor driven device precisely to a predetermined position in a short time. More particularly, this invention relates to a CD carousel loader achieving a precise and short access to the next information medium. The platter drive system is provided for an apparatus for the recording or an apparatus for the reproduction of information which uses a scanning device to read or store information or data in one or more tracks of a recording medium such as, for example, a CD, CD-ROM or DVD, an erasable CD or DVD.
CD carousel-loader devices for the recording or for the reproduction of information or data in one or more tracks of a recording medium are generally known. In order to be able to access on a desired recording medium of the CD carousel with high accuracy and speed and with a short motion time, the carousel has to be controlled in a position which makes it possible to scan or to write on the recording medium. The carousel is driven by an electric motor via a gearwheel mechanism, and the motor is switched on and off via a so-called platter motor driver IC. In accordance with the requirements made of a drive system for a carousel loader in respect of positioning accuracy, speed and self-locking, use is made of gearwheel mechanisms driven by a pinion and having high transmission. Due to complex combination of mechanical and electrical structures and elements the platter often cannot be stopped at its position precisely for its inertia. It is well known to a person skilled in the art to reduce the speed of a device to control it more precisely to a desired position. However, such a method has the disadvantage that it needs more time to reach the target position and in addition a lavish expenditure formed by mechanical or electronic braking means is necessary to control the device into the desired position.
It is an object of the invention to provide a motion control system for driving a platter in a predetermined position which requires little outlay and satisfies the requirements in respect of high positioning accuracy, short motion time and self-locking.
This object is achieved by means of the features of the invention specified in the independent claims. Advantageous developments of the invention are specified in dependent claims.
One aspect of the invention is to configure a drive system for a CD-carousel loader in such a way that a high positioning accuracy and a high speed in the course of accessing on the recording medium as well as self-locking of the drive system are ensured with little outlay.
These requirements are met by means of a motion control system which includes a braking circuit which can be formed with just a switch means which is controlled by the same terminal for switching on and off the motor. Self-locking is achieved by the use of a transmission between driving motor and platter of the carousel.
The motion control system for a CD-carousel loader is constructed in such a way that a braking circuit is added to the platter motor driver IC and the circuit which supplies the motor as well as the braking circuit are controlled by a pulse signal during a short period in front of the target position of the platter. The motion control system having a braking circuit and which controling the motor by a pulse signal during a short period in front of the target position has the advantage that by changing the constant switch on signal to a pulse signal the number of revolutions of the motor and in such a way also the velocity of the platter will be decreased in a rapid manner and a target position will be very precise and reached fast when a stop signal has been received. Finally, a shorter decelerating distance can be used with braking and, nevertheless, there is no overreaching. That means that the total duration to reach precisely the desired position will be reduced. The mechanical motion system is precisely stopped in a short time without employing any mechanical braking.
Within a preferred embodiment, a photoxe2x80x94interrupter is used to detect the positions to start the deceleration and to stop the platter. Pulses to control the motor during the deceleration period are generated continuously by a central processor unit of the recording or reproduction device until the stop point is sensed.
The braking circuit is very simple, it only comprises a transistor, a resistor and a diode, hence, it achieves the braking result with cost advantage.